The present invention is concerned with a system for supplying a compressible driving fluid to a motor of the kind comprising a housing, in which a body is reciprocable between predetermined end positions while dividing the interior of the housing into two chambers alternatingly serving as pressure chambers and receiving driving fluid from a source having a minimum pressure which substantially exceeds the fluid pressure required for driving the motor under its anticipated maximum load.
Typical examples of motors of the kind here in question are double-acting linear or rotary motors driven by compressed air, or any other gaseous fluid under pressure, in which said body is a reciprocating piston, an oscillating vane or some kind of slide, runner or the like being sealingly movable in a housing and commonly being connectable to the load to be moved. The path along which the body is moving may be rectilinear, curved or of practically any other bending or partially curved and partially rectilinear shape, provided that it permits a generally unimpeded passage of the body between the end positions. Of course, the invention is equally applicable to motors of the general kind just referred to, in which the piston or body is kept stationary whereas the housing is movable and adapted to be connected to the load.
It is essential to the invention that the source of driving fluid is not only capable of temporarily supplying the minimum pressure but also has such a large capacity in relation to the consumption of the motor that a possible pressure drop in the source during and as a result of the operation of the motor is negligible. A typical example is that the motor is driven by compressed air from a compressor unit, the capacity of which in a conventional manner is adapted to be very well sufficient for the need of the motor and, possibly, also of additional consumers connected to the compressor.
Assume for the sake of simplicity and as an example only that the motor is a compressed-air-operated, double-acting cylinder which is used for moving a load between two stations, perhaps a sliding door between closed and open positions--in which case the load is the same in both the two directions of movement--or a gripping device between a load-fetching position and a load-depositing position--in which case the load is different in the two directions of movement. Also assume, likewise only as an example, that at disposal is a compressor plant, the capacity of which so considerably exceeds the maximum consumption of the cylinder at continuous work with the highest possible speed that the risk of a pressure drop in the pressure source as a result of the consumption of the cylinder is non-existent, and that the compressor plant supplies a minimum pressure of say 800 kPa, whereas the cylinder is capable, even if only with the lowest operating speed, to carry out its intended operation at a driving fluid pressure of say 600 kPa.
In such a case the expert would probably without hesitation connect the cylinder to the compressor plant in the simpliest way, namely through a conventional directional valve, which, according to need, is either manually or automatically controlled, perhaps through a remote control circuit, and, of course, choose a cylinder with a well known fixed or variable damping, i.e. with automatic deceleration of the piston movement, adjacent the two end positions. The result would then be that the air consumption of the cylinder per time unit--disregarding possible minor leakages--is the product of the cylinder volume, the number of piston strokes performed during the selected time unit, and the conversion factor, about 8, which is required for transforming the result into normal atmospheric pressure. Possibly, although with less probability, the expert in order to reduce the air consumption would also put in a pressure regulator set at a value of 600-700 kPa before the directional valve in order to thereby correspondingly reduce the conversion factor. This, however, unavoidably results in a reduction also of the operational speed of the cylinder, i.e. an increase of the time required for the completion of each piston stroke.